Alok Misra hits on good issues around the dispute, or should I say silly dispute, about multitenancy: "There's a debate in the software industry over whether multitenancy is a prerequisite for cloud computing. "
Let's get this straight right now. Cloud computing is about sharing resources, and you can't share resources without multitenancy. Even if you have virtualization, I don't consider that alone to be cloud computing. Some multitenancy has to exist within the architecture, allowing resources to be apportioned efficiently. That point of view strikes me and to most of those in the cloud computing space as logical, but it seems to be lost on those attempting quick migrations to "the cloud," without having to put in the work.
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Alok agrees: "I sit firmly in the multitenancy camp. A multitenant architecture is when customers share an app in the cloud, while a single-tenant cloud app is similar, if not identical, to the old hosted model. But compare two subscription-based cloud apps side by side -- with the only difference being that one is multitenant and the other is single-tenant -- and the multitenant option will lower a customer's costs and offer significantly more value over time."
Why is there even a debate? The traditional on-premise vendors, as Alok points out, are moving to the cloud. These vendors are finding that building multitenant architectures is a much bigger nut to crack than they thought. Indeed, I've built three of those architectures in my career, and I can confirm that they are not at all simple to design, build, and operate.
Therefore, those moving from single-tenant on-premise architectures to multitenant cloud computing services are going to find that the transition is years in the making, not months. This is especially the case if you have to remain backward-compatible with your existing customer base.